By the time she was age 49, the breast suddenly became red, hot and swollen. "I thought something bit me," says Arnold, of Friendswood, Texas. Her doctor, diagnosing her with a pituitary gland infection, prescribed eight weeks of antibiotics.

They didn't help.

Arnold's breast swelled from a C to a D cup. "I had to buy a new bra, and pad my clothes to even them out," she says.

Months went by, and Arnold saw five doctors. Some of their explanations were stranger than others.

"One doctor said, 'You have menopause in one breast,' " Arnold says.

Eventually, Arnold arrived at Houston's M.D. Anderson Cancer Center, where she learned she had inflammatory breast cancer, or IBC, the most aggressive form of the disease. IBC takes its name from the red, inflamed condition that it produces in the breast, caused when microscopic tumor cells clog up lymph vessels.

Like most women diagnosed with IBC, Arnold had never even heard of it.

Today she tells her story often, both to educate women and doctors about a tumor that few recognize, as well as to raise funds for an "orphan disease" that gets relatively few research dollars.

Although these tumors are rare, accounting for only about 4% of breast cancer cases, they are often lethal, causing perhaps 10% of the 39,500 annual deaths from breast cancer in the USA, says Naoto Ueno, executive director of M.D. Anderson's inflammatory breast cancer research program and clinic. The median survival for women with IBC is less than three years, says Massimo Cristofanilli, chairman of medical oncology at Fox Chase Cancer Center in Philadelphia and a leading expert on inflammatory breast cancer. About 35% to 40% of patients have metastases to other organs when they're diagnosed, and 20% to 25% have metastases to their brain, Cristofanilli says.

"The vast majority will die," says Cristofanilli, who was Arnold's doctor at M.D. Anderson. In addition to her swollen breast, Arnold had cancer in 13 lymph nodes in her neck when she was diagnosed.

"They weren't sure whether to take me on as a patient or prepare me for hospice," Arnold says. "They weren't sure they could stop it before it got to my brain."

Patients often are diagnosed late, partly because their family doctors aren't familiar with IBC, Cristofanilli says.

Doctors today have no good way to detect IBC early, either. Unlike most breast cancers, IBC doesn't form a lump that's detectable on mammograms, says Cristofanilli.

IBC also grows extremely quickly. Cancer had spread from her breast to her brain by the time Gennine Chendy was diagnosed in July 2011.

"It was stage 4 inflammatory breast cancer, but I wasn't sick," says Chendy, 44, of Westchester, Pa. "You would think, that if you're walking around with a stage 4 cancer, you would be sick."

Yet even women who are diagnosed soon after symptoms develop say an IBC diagnosis can be devastating. "You're told the bad news twice," says Sachi Mallach, 39, of Bryn Mawr, Pa., who was diagnosed two years ago, shortly after suffering a miscarriage.

"You're told you have breast cancer. Then, less than a week later, I heard that not only do you have breast cancer, but you have the really aggressive breast cancer."

When Chendy was diagnosed, her only symptom was a small red mark on her breast, which she assumed was a bug bite. Chendy went for a mammogram not because of the mark, she says, but because her sister had recently been diagnosed with an early breast cancer. A savvy nurse at Fox Chase noticed the mark and helped arranged for not just a mammogram, but an ultrasound and other tests.

Within days, Chendy learned that the cancer was in her brain. Without treatment, she says, Cristofanilli gave her only six months to live. Treatment would involve chemotherapy, a double mastectomy and radiation.

"He said, 'I have a (chemo) chair. Are you ready to fight this fight?' " Chendy says. "Every person I loved was around me. I started chemo that day."

Both Chendy and Mallach were treated at Fox Chase, although they live about an hour away. Mallach, who needed two radiation treatments a day for six weeks, rented an apartment to be closer to the hospital. Chendy stayed at Hope Lodge, which provides housing to cancer patients and their families during treatment.

In September, 14 months after being diagnosed, Chendy learned that she had "no evidence of disease." In some ways, Arnold says her IBC may have saved her life.

In addition to IBC in her right breast, Arnold says tests also found the more common type of breast cancer in her left. She underwent a mastectomy and has not had reconstruction.

Because inflammatory cancers often come back, frequently spreading to the chest wall, many doctors advise against implants, for fear that they could hide early signs of a recurrence. Arnold notes that patients and doctors are reluctant to use the word "cured" with a disease this aggressive.

"I don't see myself as a cancer survivor," says Arnold, now 54, whose tests are also clear. "I am surviving."

Yet, sometimes, merely surviving isn't enough. Arnold says she wants to help other women, and help stimulate research. So she reaches out through Facebook, where she has connected with hundreds of women around the world.

Many women with IBC are too sick to attend real support groups; others simply can't find anyone else with their type of breast cancer. Last year, Arnold founded the IBC Network Foundation, a non-profit that raises awareness and money for research.

Arnold says she was inspired to venture into social media by NASA astrophysicist Susan Niebur, author of a popular blog called Toddler Planet, who died of IBC in February. Arnold's foundation is now raising money for IBC research, mostly through checks of only about $25.

The group held a "Hunt for Hope" scavenger hunt, attracting 144 people and raising $32,000, which was given to M.D. Anderson to study a common lung complication in IBC.

That may not sound like much, given that cancer trials often cost millions of dollars. But Ueno says even modest donations are important for an "orphan disease" that affects too few patients to attract much attention from pharmaceutical companies.

In some ways, Ueno says, IBC researchers are caught in a Catch-22. Scientists today know relatively little about the molecular causes of IBC, such as genes that may fuel its growth. But funding agencies these days - whether private or public - tend to favor projects in which scientists have a particular genetic target in mind, Ueno says. Yet when Ueno proposes a study to look for these underlying biological mechanisms, those grants get rejected, too.

"They say it's a fishing expedition," he says.

Yet Cristofanilli says, in some ways, research into inflammatory breast cancer is more promising today than in a long time.

That's because of research suggesting that a currently approved lung cancer drug might benefit some women with IBC.

The drug, crizotinib, sold as Xalkori, was approved last year to treat late-stage lung cancer patients with a mutation in a gene called ALK. Because some women with IBC have these mutations, scientists are now running clinical trials to see if the drug could help control their disease, as well, says Cristofanilli.

Scientists are testing several other experimental drugs that may target key genetic mutations in IBC, as well. Cristofanilli says his research is driven not just by the desire to solve a scientific question, but to help women with so few options.

Women with IBC, he notes, tend to be several years younger than the average breast cancer patient, and many are raising families. Many are African-American. And because IBC is more common among women who are overweight or obese, Cristofanilli says he's concerned it could become more common.

"It affects a part of the population that is very active," Cristofanilli says. "These families are left without their wives, without their mothers. ... This particular group of women deserves better."